As is known, a heliostat is a device used to follow the Sun's route during the span of the day, usually to orient the light thereof towards a precise target thanks to the help of one or more mirrors.
Today heliostats are mostly used in industrial thermodynamic processes to increase the temperature of thermal devices on towers, by the simultaneous use of several heliostats pointing at the same target, which are indispensable to obtain the necessary temperatures for devices that convert heat into electricity.
However, other applications for heliostats may include light-redirection for domestic and city uses, in which the heliostat redirects sunlight towards an object, room, street, monument or piazza to illuminate, brighten and/or warm.
Most sunlight redirection systems in use today are expensive and require intensive and invasive installation procedures that could be obviated by the subtle use of heliostats.
However, if one wanted to use a heliostat as a domestic device to place indoors (on a window sill, kitchen-island, desk, nightstand, wall or ceiling to name a few options) or outdoors (balcony railing or garden for example) in order for such domestic device to be in direct contact with the sun that it then is able to redirect where sunlight is most needed, which could be indoors (on the ceiling to obtain a diffuse lighting effect thanks to the scattering provided by the ceiling material or in specific parts of the building to obtain a task-based lighting effect such as to illuminate a specific area of the building like a desk or a plant) or outdoors (on patios or backyards that are in the shade and require sunlight), the heliostat systems in use today would prove to be rather inadequate. Most heliostats, in fact, focus on emphasizing and optimizing the features that are fundamental in industrial applications, such as pointing accuracy, planarity of the mirror, stability and robustness of the mechanics. But other features become important when developing a heliostat for domestic applications, such as but not limited to compactness, portability, self-powered autonomy, lightness, low maintenance times, low-cost of the entire system and protection from outside weather.
In order to create a heliostat that is optimized for domestic use one needs to revisit the key components that make a heliostat and re-arrange them so that optimization of the domestic features are emphasized.
U.S. Pat. No. 4,192,583 to Horton defines a heliostat assembled within a protective enclosure supported by a foundation mounted in the ground. While this is a means of protection from weather elements, such an enclosure does not allow for the portability required of a heliostat for residential indoor as well as outdoor use.
U.S. Pat. No. 4,283,887 to Horton et al. defines a bubble-like enclosure for a heliostat that is inflated by filling it with pressurized air. Whilst this patent clearly defines a means of protection of the heliostat contained within such an enclosure, it is in no way addressing any of the other features of compactness, portability, self-powered autonomy, low-maintenance time or low-cost. In fact, such a protective structure is intended for larger heliostats that need to be installed on the ground and are supported by a foundation in the form of a soil filled, plastic ring-bag mounted in the ground at the heliostat site.
U.S. Pat. No. 4,620,382 to Sallis teaches an apparatus for pneumatically or hydraulically tensioning a membrane, which stretched membrane can support a reflective surface for use as a heliostat in a solar energy collection system. A disadvantage to this type of heliostat device is the absence of an enclosure to protect the heliostat device from outside elements.
U.S. Pat. No. 4,870,949 to Butler teaches a wind resistant, two axis tracker that is used to direct a solar reflector, heliostat, or dish antenna. An elevation drive ring is supported in a vertical orientation by dolly wheels rotatably attached to a base. The reflector is attached at two points along the circumference of the elevation drive ring. In the preferred embodiment, a reflector having a diameter slightly less than the inside diameter of the elevation drive ring is mounted to the elevation drive ring. A number of support members, such as cables, extend from the elevation drive ring to the periphery of the reflector. Azimuth adjustment is either provided by incorporating a horizontal turntable or drive ring as part of the base, or by pivoting the reflector within the elevation drive ring by adjusting the respective lengths of the support cables extending laterally from the elevation drive ring to the periphery of the reflector. Drawbacks with this type of heliostat device is that it does not include an enclosure to protect the heliostat device and is primarily concerned with using a centerless elevation drive combined with a turntable azimuth drive for reflectors in order to reduce the structure/weight of materials for wind resistance. This may be suitable under extreme conditions, such a design would be impractical and ineffective for the domestic use of a scaled down heliostat device.
U.S. Pat. No. 7,887,188 to Knight, while disclosing a heliostat comprised of a mirror that is placed in two hemispheres that are joined together, wherein the mirror contains a plurality of wheels that run on the inner surface of the sphere so as to move it and orient it towards the target, it manages to maximize the mirror size that can be fit inside the sphere but completely fails at providing an optically smooth surface for the inbound and outbound sunlight, where by inbound one means the sunlight from the sun to the mirror and by outbound the sunlight reflected from the mirror to the target. Such a hemisphere joint does not allow both inbound and outbound sunlight to enter or exit unhindered from the disclosed enclosure. This would confuse any optical sensor that based its accuracy on the angle created by the incoming and outgoing rays if those rays are deviated in their path by a significant refractivity effect. More importantly, in operation the frictional contact between the wheels and the sphere's inner surface would inevitably start to leave marks on the inner surface and over time these would not only become unsightly, but would also negatively affect the optical performance of the heliostat.
U.S. Pat. No. 8,132,928 to Bronstein et al. describes an improved solar reflector utilizing a tensioned reflective membrane, further including a membrane attached to the outer surface of a metal strap that is positioned on an end form by means of a curved-face tensioning block. While linear tensioned membrane reflectors have some advantages over more rigid structures, such membranes present a variety of problems compared to those reflector technologies using more rigid frames. For example, most membranes utilize certain laminates, such as films, as a substrate for the membrane. Mylar (Biaxially-oriented polyethylene terephthalate boPET polyester film) is a dimensionally stable material that reacts in undesirable ways when the film is placed under compression. A typical means of mounting the membrane is to adhere it to the underside of a metal strap with a structural adhesive, such as epoxy. The strap is then wrapped around the end form and clamped in place. However, as the strap is bent around the end form the strap's inward facing surface and the membranes are placed in compression, wrinkles are produced. Such defects are then crushed and locked in place as the strap is tightened on the end form. These distortions in the film are magnified by the film and transmitted into the membrane as large longitudinal wrinkles and ripples that span across the entire membrane's surface, distorting its shape and resulting in a diminished performance for its intend purpose.
There is a need in the art to provide a solution to the large scale heliostats that are incapable, unsuitable and impractical for domestic use while simultaneously providing for enhanced benefits when compared to the state of the art in heliostats.